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[Qemu-devel] [PATCH] block: Formats don't need CONSISTENT_READ with NO_I

From: Kevin Wolf
Subject: [Qemu-devel] [PATCH] block: Formats don't need CONSISTENT_READ with NO_IO
Date: Thu, 30 Nov 2017 17:44:01 +0100

Commit 1f4ad7d fixed 'qemu-img info' for raw images that are currently
in use as a mirror target. It is not enough for image formats, though,
as these still unconditionally request BLK_PERM_CONSISTENT_READ.

As this permission is meaningless unless you do actual I/O on the image,
drop the requirement and allow 'qemu-img info' even for image formats
under conditions where BLK_PERM_CONSISTENT_READ can't be granted.

Signed-off-by: Kevin Wolf <address@hidden>
 block.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 9a1a0d1e73..ddb6836c52 100644
--- a/block.c
+++ b/block.c
@@ -1924,6 +1924,8 @@ void bdrv_format_default_perms(BlockDriverState *bs, 
BdrvChild *c,
     assert(role == &child_backing || role == &child_file);
     if (!backing) {
+        int flags = bdrv_reopen_get_flags(reopen_queue, bs);
         /* Apart from the modifications below, the same permissions are
          * forwarded and left alone as for filters */
         bdrv_filter_default_perms(bs, c, role, reopen_queue, perm, shared,
@@ -1936,7 +1938,9 @@ void bdrv_format_default_perms(BlockDriverState *bs, 
BdrvChild *c,
         /* bs->file always needs to be consistent because of the metadata. We
          * can never allow other users to resize or write to it. */
-        perm |= BLK_PERM_CONSISTENT_READ;
+        if (!(flags & BDRV_O_NO_IO)) {
+            perm |= BLK_PERM_CONSISTENT_READ;
+        }
         shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
     } else {
         /* We want consistent read from backing files if the parent needs it.

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